The present invention relates to the manufacture of pipes, and more particularly to apparatus for the manufacturing of continuous lengths of metal pipe from a flat metal strip.
Stationary and mobile pipe forming devices for making a continuous length of metal pipe from flat metal strip material are well known in the prior art. See, for example, descriptions of mobile pipe forming mills in Vassar U.S. Pat. No. 3,014,118, issued Dec. 19, 1961; Sprung et al., U.S. Pat. No. 3,145,758, issued Aug. 25, 1964; Tsuyama, et al., Canadian Pat. No. 1,160,436, issued Jan. 17, 1984, Anderson Canadian Pat. No. 1,119,849, issued Mar. 16, 1982; and Ferreroele, Canadian Pat. No. 627,513, issued Sept. 19, 1961.
It is extremely important in such line pipe mills to ensure that the temperature of the weld is maintained within an appropriate range. If the weld becomes too hot or is heated too long, the edges of the metal strip being welded will fold or there will be burn through. If the weld temperature is too low or the weld is not heated long enough, a cold weld results. In either case, testing of the pipe from the mill would reject such a pipe. The improperly welded section of pipe would have to be cut and a properly welded one reinserted. Most of these prior art mobile and stationary pipe mills have not had proper temperature control for the weld.
As well, particularly for mobile pipe making apparatus, it has been necessary for the operator to control the speed of pipe making and also the rate of progress of the mill-carrying vehicle. It is necessary to consistantly and accurately match these two speeds, in opposite directions, to ensure that the ground speed of the pipe issuing from the rear of the mill is exactly zero. When this situation does not exist, the production of downgraded pipe results, again this pipe having to be cut out and replaced. If the pipe is made faster than the vehicle is advancing, it backs up and tries to push the mill-carrying vehicle, causing slowdown of the pipe mill and burn through of the weld. If the vehicle is going too fast relative to the pipe mill, the pipe is pulled through the mill too fast with the result that the drives on the vehicle risk becoming sheared, or portions of the pipe are cold welded or skidded on the ground and damaged, necessitating additional cut outs. In either case such cut outs slow down the pipe line manufacture and increase production costs.
Additionally, problems of manoeuvrability and weight exist in prior art mobile line pipe mills, particularly where a two vehicle apparatus has been used. Such devices turn and back up often with great difficulty, and have trouble moving over uneven, spongy or muddy terrain such as in tundra or swamp areas.
It is an object of the present invention to provide an improved pipe mill which overcomes many of the problems of such prior art mills. While the present invention will be described particularly in relationship to a mobile pipe mill in which pipe is made in one direction while a vehicle on which the mill is carried moves at equal speed in the opposite direction, it will be clear to one skilled in the art that many of the aspects of the present invention may be applied to stationary pipe mills.